a) Field of the Invention
The present invention is directed to a jack plug and, more particularly, a jack plug with a contact bulb provided at its free end having a contact shaft serving for the electrical connection of an electrical conductor.
b) Background Art
A great number of jack plugs of the most varied constructions are known. These numerous constructional forms are relatively costly and complicated (U.S. Pat. No. 3,656,089, U.S. Pat. No. 4,275,947, U.S. Pat. No. 4,335,930, U.S. Pat. No. 4,647,135, RPS 561 322).
A jack plug is known from German Offenlegungsschrift 15 38 34 172 in which a tubular shaft serves as external contact and which has a portion having a greater diameter than this shaft which is constructed as a single piece. The portion, however, carries an external thread adjacent to the aforementioned shaft. A gripping sleeve is screwed onto the external thread and covers the aforementioned portion. No functional cooperation between the portion and the gripping sleeve is provided or ascertainable. The portion is indented at diametrically opposite sides to provide pull relief for the cable and to make electrical contact between the external contact and the cable sheath. The indentations press on the inserted cable and its sheath, which is exposed in this location, so as to hold and clamp the cable.
Comparable constructions are shown in U.S. Pat. No. 4,196,958 and U.S. Pat. No. 4,275,947. The free end of the portion has short notches extending over only part of the axial length of the portion. The region having the notches is further provided with an external thread. A gripping sleeve whose axial length does not exceed approximately to the axial length of the portion carries an internal thread at its inner side remote from the contact bulb and can be screwed onto the external thread at the free, slotted end of the aforementioned portion. The free edges of the portion are tapered or beveled conically. When the gripping sleeve is screwed on, the edge of the cable insertion bore hole of the gripping sleeve contacts the beveled edge As a result of the cooperation of these parts, the short tabs formed by the notches are pressed together somewhat when the gripping sleeve is tightened and screwed on and thus grasp the cable running through the portion in a clamping manner.
In the construction according to U.S. Pat. No. 4,196,958, the contact shaft which communicates with the contact bulb so as to be electrically conducting is so long that it projects beyond the insulating tube and into the interior of the plug, i.e., into the portion which extends beyond the inner end of the insulating tube and has a diameter which is greater than that of the shaft serving as external contact, although this portion is constructed so as to form one piece with the latter. The portion of the contact pin projecting beyond the insulating tube has a recess for receiving the free inner end of the conductor. The conductor end is either soldered or crimped. Cut out portions through which a tool can be inserted for connecting the aforementioned conductor end with the contact shaft are provided in the portion. In one instance, crimping tools are inserted through the aforementioned cut out portions; in another case, the solder and soldering iron are inserted through these openings.
These previously known constructions have disadvantages: the gripping sleeve, to the extent that it is constructed in one piece, is only supported on one side in this case and extends over the aforementioned portion in a cantilevering manner. If the inside of the gripping sleeve is to contact the outside of the portion for the purpose of stabilizing the construction as a whole, the gripping sleeve must be constructed in two parts. Since the relatively short notches and the external thread on the portion overlap, the tabs formed by the notches can only exert their pincer function to a limited extent because the more the tabs are pressed in radially, the weaker the engagement of the coupled threads.